Report on the selection of the reference XT-ADS target design and specifications

The XT-ADS is an experimental accelerator driven system (ADS) that is being developed in the framework of the European FP6 EUROTRANS project. In this deliverable, the specifications of the spallation target and the selection of its reference design are discussed. Justification of the design options, in relation to the performance requirements of the XT-ADS and the interlinking with the design of the sub-critical core and the primary system, are given

Modal characteristics of a flexible tube in turbulent axial flow: a numerical approach and validation with experimental data

Flow-induced vibration is an important concern in the design of tube bundles. Due to the coupling of fluid motion and structural motion, instabilities such as flutter and divergence can arise. Next to the instabilities caused by the coupling of fluid motion and structural motion, turbulence could cause small amplitude vibrations, which in turn could give rise to long-term damage. Currently, the dynamical behavior of a tube in axial flow is studied by splitting the flow forces into inviscid and viscous components. The inviscid flow forces are determined from potential flow theory while the viscous flow forces come from empirical formulations. In this paper, a computational methodology is proposed to improve the accuracy of the predicted dynamical behaviour. In this methodology partitioned fluid-structure interaction simulations are performed to calculate the free vibration decay of a tube in axial flow. The tube is initially deformed according to an eigenmode in vacuum. Modal characteristics are then derived from the free vibration decay of the tube surrounded by the turbulent water flow. To validate this computational methodology a series of experiments is reproduced. In these experiments the frequency and damping of the fundamental mode of a solid brass cylinder were measured

Coupled system thermal Hydraulics/CFD models: General guidelines and applications to heavy liquid metals

This work aims to review the general guidelines to be adopted to perform coupled System Thermal Hydraulics (STH)/CFD calculations. The coupled analysis is often required when complex phenomena characterized by different characteristic time and length scales are investigated. Indeed, by STH/CFD coupling the main drawbacks of both stand-alone codes are overcome, reducing the computational cost and providing more realistic solutions. A review of several works available in literature and involving different coupling approaches, codes, time-advancing schemes and application fields is given. Besides STH/CFD coupling techniques, spatial domains and numerical schemes are analysed in detail. A brief description of applications to heavy liquid metal systems is also reported; lessons drawn in the frame of these and other works are then considered in order to develop a set of good practice guidelines for coupled STH/CFD applications

The influence of the ectomycorrhizal fungus Rhizopogon subareolatus on growth and nutrient element localisation in two varieties of Douglas fir (Pseudotsuga menziesii var. menziesii and var. glauca) in response to manganese stress

Acidification of forest ecosystems leads to increased plant availability of the micronutrient manganese (Mn), which is toxic when taken up in excess. To investigate whether ectomycorrhizas protect against excessive Mn by improving plant growth and nutrition or by retention of excess Mn in the hyphal mantle, seedlings of two populations of Douglas fir (Pseudotsuga menziesii), two varieties, one being menziesii (DFM) and the other being glauca (DFG), were inoculated with the ectomycorrhizal fungus Rhizopogon subareolatus in sand cultures. Five months after inoculation, half of the inoculated and non-inoculated seedlings were exposed to excess Mn in the nutrient solution for further 5 months. At the end of this period, plant productivity, nutrient concentrations, Mn uptake and subcellular compartmentalisation were evaluated. Non-inoculated, non-stressed DFM plants produced about 2.5 times more biomass than similarly treated DFG. Excess Mn in the nutrient solution led to high accumulation of Mn in needles and roots but only to marginal loss in biomass. Colonisation with R. subareolatus slightly suppressed DFM growth but strongly reduced that of DFG (−50%) despite positive effects of mycorrhizas on plant phosphorus nutrition. Growth reductions of inoculated Douglas fir seedlings were unexpected since the degree of mycorrhization was not high, i.e. ca. 30% in DFM and 8% in DFG. Accumulation of high Mn was not prevented in inoculated seedlings. The hyphal mantle of mycorrhizal root tips accumulated divalent cations such as Ca, but not Mn, thus not providing a barrier against excessive Mn uptake into the plants associated with R. subareolatus

Characterisation in water experiments of a “detached flow” free surface spallation target

In the development of accelerator driven systems, ADS, free surface lead–bismuth spallation targets are considered as promising solutions due to their possibility for compactness, their lifetime, and their ability to transport the heat deposited by the proton beam away from the spallation zone. Experiments to characterise the hydraulics of the targets are needed to allow the validation of numerical models and to improve the design. Such experiments have been performed in water on a new concept labelled “detached flow” geometry. This name was chosen because the liquid undergoes a free fall between the nozzle exit where the main free surface (that separating the void of the beam line from the liquid) is created and a second free surface downstream. The void surrounding the liquid jet plays the role of a buffer. The experiments show that a very stable main free surface with a small recirculation is obtained using this geometry thanks to the presence of the second free surface and the nozzle geometry. The experiments confirm that the level of the second free surface has no influence on the characteristics of the main free surface, improving the main free surface control. The influences of the mass flow rate and of the inlet velocity are evaluated. The free surface level rises linearly with an increase in mass flow rate. The recirculation zone is also stronger in this case. The opposite is found when the mass flow rate is decreased. For all mass flow rates studied, a stable free surface is obtained. Moreover, the outer shape of the liquid jet is similar at all mass flow rates. It is only dictated by the nozzle exit angle. Increasing slightly the inlet velocity for a given mass flow rate has a positive effect on the recirculation stability. The “detached flow” target is a promising design for ADS

Report on the selection of the reference XT-ADS target design and specifications

The XT-ADS is an experimental accelerator driven system (ADS) that is being developed in the framework of the European FP6 EUROTRANS project. In this deliverable, the specifications of the spallation target and the selection of its reference design are discussed. Justification of the design options, in relation to the performance requirements of the XT-ADS and the interlinking with the design of the sub-critical core and the primary system, are given

Simulation of fuel dispersion in the MYRRHA-FASTEF primary coolant with CFD and SIMMER-IV

The objective of this work is to assess the behavior of fuel redistribution in heavy liquid metal nuclear systems under fuel pin failure conditions. Two different modeling approaches are considered using Computational Fluid Dynamics (CFD) codes and a system code, applied to the MYRRHA facility primary coolant loop version 1.4. Two different CFD models are constructed: the first is a single-phase steady model prepared in ANSYS Fluent, while the second is a two-phase model based on the volume of fluid (VOF) method in STARCCM+ to capture the upper free-surface dynamics. Both use a Lagrangian tracking approach with oneway coupling to follow the particles throughout the reactor. The system code SIMMER-IV is used for the third model, without neutronic coupling. Although limited regarding the fluid dynamic aspects compared to the CFD codes, comparisons of particle distributions highlight strong similarities despite quantitative discrepancies in the size of fuel accumulations. These disparities should be taken into account while performing the safety analysis of nuclear systems and developing strategies for accident mitigation